Catalyst flow sensor

ABSTRACT

A catalyst alarm system for resin/catalyst spray applications, the system having a first flow sensor that monitors whether a catalyst from a manifold is flowing for supply to a spay gun or other applicator at a specified minimum rate; a second flow sensor that detects if the catalyst is flowing out of a bypass conduit of the manifold, which indicates the catalyst is not being mixed with the resin; a third flow sensor that detects if the catalyst is flowing out of an over-pressure conduit of the manifold, which indicates that only a partial amount of the required catalyst is being mixed with the resin; and monitoring circuitry for providing alarm and/or control features based on activation combinations of the three flow sensors.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.62/573,850 filed Oct. 18, 2017, entitled Catalyst Flow Switch with FlowAlarm, incorporated herein by reference in its entirety.

FIELD

This invention relates to catalyst delivery systems for short-fibercomposite manufacturing processes. More particularly, this inventionrelates to catalyst flow sensors and associated methods and alarmsystems that indicate and provide an alarm when catalyst is not flowingin a correct manner.

BACKGROUND

Liquid resins and catalysts used for spray applications associated withshort-fiber composite manufacturing processes are typically mixed justbefore spraying and it is important to maintain the flows in desiredamounts. The catalyst is an initiator for a polymerization reaction withthe resin and the catalyst is typically highly reactive. Conventionalflow sensors are unsuitable for use with highly reactive catalyst fluidsand their typical process conditions involving high pressures.

Prior flow sensors have been found to be incompatible for use withcatalysts due to the highly reactive nature of catalysts such as methylethyl ketone peroxide (MEKP), and high-pressure conditions, such as upto about 1500 psi, typically associated with such spray processes.Accordingly, what is desired is a flow sensing apparatus that issuitable for monitoring the flow of a liquid catalyst and for signalingwhen the flow is outside of a desired range.

The present disclosure advantageously provides catalyst flow sensors andassociated delivery systems configured for use with liquid catalysts todetect when the flow rate of the catalyst is outside of a desired range.The sensors are configured for use with reactive catalysts under highpressure conditions, and the systems advantageously include an alarm orother indicators designed to alert a user when catalyst is not flowingas desired.

SUMMARY

The disclosure relates to liquid flow sensors, methods for monitoringliquid flows, and to flow monitoring systems.

In one aspect, the disclosure relates to a liquid flow sensor thatincludes an elongate flow tube having an inlet end and an outlet end.Liquid flows into the flow tube at the inlet end and exits from theoutlet end. A float is located in the flow tube and configured for theliquid flowing in the flow tube to flow around the float, the floatincluding a magnet. An electrical circuit is proximate the flow tube.The electrical circuit includes a magnetic sensor located proximate thefloat for sensing a position of the magnet in the flow tube. Theposition of the magnet in the flow tube is related to the position ofthe float in the flow tube, which is related to flow characteristicsassociated with flow of the liquid through the flow tube.

In another aspect, the disclosure provides a method of monitoring flowof a liquid. The method includes the steps of flowing a liquid underpressure through an elongate flow tube having an inlet end and an outletend, wherein the liquid flows into the flow tube at the inlet end andexits at the outlet end; providing a float including a magnet in theflow tube, the float configured so that the liquid flowing in the flowtube flows around the float; directing the flow of liquid through theelongate flow tube to contact and flow around the float such that theposition of the float in the flow tube is dependent upon the flow ofliquid through the flow tube; and sensing a position of the magnet inthe flow tube. The position of the magnet in the flow tube is related tothe position of the float in the flow tube, which is related to flowcharacteristics associated with flow of the liquid through the flowtube.

In a further aspect, the disclosure relates to a flow monitoring system.The system includes a source of pressurized liquid capable of providinga feed flow of the liquid, or a recirculating flow of a liquid, or anoverpressure flow of the liquid, or combinations thereof. The systemalso includes a first flow sensor for receiving the feed flow of theliquid, a second flow sensor for receiving the recirculating flow of theliquid, and a third flow sensor for receiving the overpressure flow ofthe liquid. Each of the first, second and third flow sensors include aflow tube having a float located in the flow tube and configured forliquid flowing in the flow tube to flow around the float. Each floatincludes a magnet.

The system also includes an electronic circuit. The electronic circuitincludes (i) a first magnetic sensor located proximate the first flowsensor for sensing a position of the magnet in the float of the firstflow sensor, wherein the position of the magnet in the flow tube of thefirst flow sensor is related to flow characteristics associated with thefeed flow of the liquid through the first flow sensor, (ii) a secondmagnetic sensor located proximate the second flow sensor for sensing aposition of the magnet in the float of the second flow sensor, whereinthe position of the magnet in the flow tube of the second flow sensor isrelated to flow characteristics associated with the recirculating flowof the liquid through the second flow sensor, and (iii) a third flowsensor for sensing a position of the magnet in the float of the thirdflow sensor, wherein the position of the magnet in the flow tube of thethird flow sensor is related to flow characteristics associated with theoverpressure flow of the liquid through the third flow sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the disclosure are apparent by reference to thedetailed description when considered in conjunction with the figures,which are not to scale so as to more clearly show the details, whereinlike reference numbers indicate like elements throughout the severalviews, and wherein:

FIG. 1 is a perspective view showing a catalyst flow sensor according tothe disclosure.

FIG. 2 is a cross-sectional view of a catalyst flow sensor arrayaccording to the disclosure.

FIG. 3 shows a front panel of the catalyst flow sensor array of FIG. 2.

FIGS. 4-6 are interior views of the catalyst flow sensor array of FIG.2.

FIGS. 7A-7C show dimensions of components of the catalyst flow sensorarray of FIG. 2.

FIG. 8A is a perspective view of a float component of the catalyst flowsensor array of FIG. 2.

FIGS. 8B and 8C show dimensions of the float component.

FIG. 9 is a perspective view showing additional components of thecatalyst flow sensor array of FIG. 2.

FIG. 10 depicts a flow chart of alarm logic for the catalyst flow sensorarray of FIG. 2.

FIG. 11 depicts an alternate flow chart of alarm logic for the catalystflow sensor array of FIG. 2.

DETAILED DESCRIPTION

With initial reference to FIG. 1, there is shown a flow sensor 10according to the disclosure and configured for use with liquid catalystsand designed to detect when the flow of catalyst is outside ofpredetermined parameters. An example catalyst is a water-soluble organicperoxide known as methyl ethyl ketone peroxide (MEKP). MEKP has aviscosity at 20 degrees C. of 31 mPas.

The flow sensor 10 and the devices described herein that incorporatesuch flow sensors are desirable for use on the supply line of a catalystto be mixed with a resin via a spray applicator for short-fibercomposite manufacturing processes. In these processes, the resin and thecatalyst are mixed just before application/spraying and it is importantto maintain the flows in desired amounts. The present disclosure relatesto monitoring of the flow of the catalyst, which is typically suppliedat a pressure of about 1,500 psi.

The flow sensor 10 includes a catalyst flow tube 12 formed as bymachining the flow tube 12 through a block of metal such as stainlesssteel. Catalyst flows through the flow tube 12 in the direction of arrowA from a source of catalyst toward a spray gun, nozzle or otherapplicator device. For example, a catalyst pump provides a pressurizedflow of catalyst via tubing into an entrance end 12 a of the flow tube12 for exit via tubing connected to an exit end 12 b of the flow tube toa spray nozzle or applicator device. Typically, mixing of resin andcatalyst occurs within the spray nozzle or applicator device.

A float 14 having a magnet 16 embedded therein is located within thecatalyst flow tube 12. The float 14 is desirably cylindrical and sizedsmaller than the catalyst flow tube 12 to provide a fluid gap 18 betweenthe float 14 and the interior sidewall of the catalyst flow tube 12.

The flow sensor 10 includes an enclosure (not shown), desirably of metaland attached to the block of metal through which the flow tube 12 ismachined, for housing an electrical control circuit such as a circuithaving a microcontroller 22 and a giant magnetoresistance (GMR) sensor24 located in proximity to the magnet 16 so as to be able to detect thelocation of the magnet 16 in the float 14 in the catalyst flow tube 12.The enclosure serves to protect the internal circuitry from thepotentially reactive environment associated with resin/catalyst sprayoperations.

The GMR sensor 24 is a multilayer sensor having alternatingferromagnetic and non-magnetic conductive layers. In broad overview, thesensor 24 detects the magnetic field of the magnet 16, and detectschanges in the magnetic field corresponding to changes in position ofthe magnet 16.

When the flow sensor 10 is in use to detect the flow of catalyst, thefloat 14 will rise if the minimum flow rate of the catalyst is such thatthe forces generated in the fluid gap caused by the shearing of thefluid between the float 14 and the flow tube 12 are sufficient toovercome the combined weight of the float 14 and the magnet 16 embeddedin the float 14. Thus, the position of the float 14 will vary based onthe flow rate of the catalyst. The sensor 24 detects the position of thefloat 14 in the flow tube 12 and generates output signals correspondingto the detected position of the float 14.

The float 14 will be located in a desired range of positions if the flowrate of the catalyst is within a desired range. In the event theposition of the float 14 is detected by the sensor 24 to be outside ofthe desired range of positions, the microcontroller 22 may cause thegeneration of an alarm signal, such as an audible or visual alarm orboth.

The geometry and dimensions of the float 14 are selected relative to theviscosity and the flow rates expected for the catalyst, and relative tothe geometry of the flow tube 12. The float 14 cooperates with the flowtube 12 and the flow of the catalyst to be in a desired range ofpositions for desired flow rates of a particular catalyst through theflow tube 12.

The flow sensor 10 advantageously utilizes magnetic fields and fluidshear forces of the catalyst to indicate when desired minimum flow ofthe catalyst is achieved. The sensor 10 also advantageously avoids theuse of seals and rotating parts that are prone to corrosion and/orfailure when exposed to reactive catalyst fluids.

In a preferred embodiment, as shown in connection with FIGS. 2-9, a flowsensor array 30 incorporates a plurality of flow sensors 30 a, 30 b and30 c to provide a catalyst flow monitoring and alert system according tothe disclosure preferably having visual and audible alerts. The flowsensors 30 a, 30 b, and 30 c each substantially correspond to the flowsensor 10 and include a catalyst flow tube 32 through which catalystflows in the direction of the arrow A, and a float 34 having a magnet 36embedded therein. The flow tubes 32 may be formed by machining the flowtubes 32 through a block of metal 38 such as stainless steel.

Flow sensors 30 a-30 c are used for sensing different aspects ofcatalyst flow for the array 30. For example, the flow sensor 30 a isutilized to determine if the catalyst is flowing at least a desiredminimum rate. The flow sensor 30 b is utilized to determine if catalystis flowing out a bypass valve of the array 30, which indicates that thecatalyst is not being mixed with the resin. The flow sensor 30 c isutilized to determine if catalyst is flowing out of an over-pressureoutlet, which indicates that only a partial amount of the requiredcatalyst is being mixed with the resin.

The flow sensor array 30 includes an enclosure 40, desirably of metal,that is bolted to the block of metal 38 through which the flow tubes 32are machined. The enclosure 40 includes an electrical control circuitsuch as a circuit board 42 having a microcontroller 42 a including aplurality of giant magnetoresistance (GMR) sensors 44, one located inproximity to each of the magnets 36 so as to be able to detect thelocation of the floats 34 having the magnets 36 in the catalyst flowtubes 32 of the flow sensors 30 a-30 c. The microcontroller 42 with thesensors 44 function to read the positions of the floats 34 of the flowsensors 30 a-30 c and alert an operator if any noteworthy states, suchas fail states exist in any of the flow sensors 30 a-30 c and, if so, inwhich flow sensor the fail state has occurred.

As shown in FIG. 9, the catalyst is supplied from a source of catalystby a catalyst pump 50 or the like to provide a pressurized flow ofcatalyst. The catalyst is fed initially to a manifold 52 having a supplyoutlet 54 a, a recirculation outlet 54 b, and an overpressure outlet 54c. These manifold outlets 54 a-54 c are connected via tubing 56 a, 56 b,and 56 c, respectively, to input connectors of the flow sensors 30 a-30c, respectively, for travel of catalyst to the array 30, and through theflow sensors 30 a-30 c.

Catalyst exiting the flow sensor 30 a is routed via tubing to the spraygun, nozzle or other applicator device for mixing with the resin forapplication. The applicator device is typically pneumatic and exhaustsair during operation. As described in more detail below, the exhaust airof the applicator device is harnessed and routed to an applicator airinput 58 of the array 30 to be used to indicate to the array 30 when aspraying operation is being conducted.

During a spraying operation, the float 34 of the flow sensor 30 a willrise if the minimum flow rate of the catalyst through the flow sensor 30a is such that the forces generated in the fluid gap caused by theshearing of the fluid between the float 34 and the flow tube 32 aresufficient to overcome the combined weight of the float 34 and themagnet 36 embedded in the float 34. The associated sensor 44 detects theposition of the float 34 in the flow tube 32 of the flow sensor 30 a andgenerates output signals corresponding to the detected position of thefloat 44. Likewise, if catalyst flows from the recirculation outlet 54 bto the flow sensor 30 b and/or catalyst flows from the overpressureoutlet 54 c to the flow sensor 30 c, these flows of catalyst will act onthe floats 34 of the flow sensors 30 b and 30 c and be detected by theassociated sensors 44 in a similar manner.

As noted above, the geometry and dimensions of the floats 34 areselected relative to the viscosity and the flow rates expected for thecatalyst, and for the geometry of the flow tubes 13 so as to cooperateto enable the floats 34 to be in a desired range of positions fordesired flow rates of a particular catalyst. A preferred catalyst isMEKP having a viscosity of 31 mPas at 20 degrees C. The flow rate of thecatalyst preferably ranges from about 0.65 fluid ounces per minute toabout 19 fluid ounces per minute with a minimum flow rate of about 0.5fluid ounces per minute.

With reference to FIGS. 7A-7C, the catalyst flow tubes 32 of the flowsensors 30 a-30 c are desirably arranged and dimensioned as shown foruse with the described catalyst.

With reference to FIGS. 8A-8C, the floats 34 and the magnets 36 of theflow sensors 30 a-30 c are configured as shown for use with thedescribed catalyst and flow tubes 32. The floats 34 preferably include aslot 34 a on the bottom thereof and a top 34 b that is flat with roundededges. The slot 34 a advantageously enables catalyst fluid to flow inthe opposite direction and prevents the float 34 from sealing against alip in the flow tube 32. The top 34 b advantageously reduces frictionalflow coefficients of the float 34.

The floats 34 are desirably made of 316 grade stainless steel with aweight of about 1.8 grams. The magnets 36 are preferably cylindrical andcharacteristics of a desirable magnet for use in providing the magnets36 are set forth in Table 1 below:

TABLE 1 Dimensions: ⅛ inch diameter by ½ inch thick Tolerances +/−0.004inch × +/−0.004 inch Material NdFeb, grade N52 Plating/Coating Ni—Cu—Ni(Nickel) Magnetization Direction Axial (Poles on Flat Ends) Weight0.0266 ounces (0.754 grams) Pull Force, Case 1 1.08 pounds Pull Force,Case 2 1.09 pounds Surface Field 7343 Gauss Max Operating Temperature176° F. (80° C.) Brmax 14,800 Gauss Bhmax 52 MGOe

To power the circuit board 42, electrical power, preferably 12-voltdirect current, may be supplied to the flow sensor array 30 via a powerinput 60 in electrical communication with a power supply, generallyindicated with reference numeral 62 (FIG. 9). The power supply 62 ispreferably provided by a 110-volt alternating current to 12-volt directcurrent power supply integrated into a cord that may be plugged into anelectrical outlet, preferably 110-220 VAC 50-60 Hz. Electrical power isconnected from the power supply 62 to the circuit board 42 via a powerinput terminal 64 on the circuit board 42 (FIG. 4). When electricalpower is supplied to the circuit board 42, a power indicator lamp 66 isdesirably illuminated to indicate to an operator that power has beensupplied.

Lights or other visual indicators 70 a, 70 b, and 70 c are provided toindicate if an undesirable flow of catalyst is detected by any of theflow sensors 30 a-30 c, respectively. In this regard, indicator 70 ailluminates if the array 30 is powered and the flow of catalyst asdetected by the flow sensor 30 a is below the desired minimum flow.Indicators 70 b and 70 c illuminate when flow of catalyst occurs throughthe flow sensor 30 b and 30 c, respectively as explained more fullybelow. The indicators 70 a-70 c are connected to the circuit board 42 byan indicator terminal 72 and are controlled by the microcontroller 42 ain response to signals received from the flow sensors 30 a-30 c.

With reference to FIG. 4, an audible alarm such as a whistle 80, whichmay be remote from the enclosure 40 is provided to indicate if anundesirable flow of catalyst is detected by any of the flow sensors 30a-30 c, respectively. Upon hearing the alarm, the operator may look tothe visual indicators to determine the cause of the alarm. The whistle80 is air operated due to the reactive environment. Air is supplied intothe array 30 via an alarm inlet air port 82 a and routed from the arrayvia an alarm outlet air port 82 b. The alarm inlet air is routed fromthe port 82 a to a solenoid valve 84 via conduit 86 a and from the valve84 to the port 82 b by conduit 86 b. The valve 84 is connected to thecircuit board 42 by a valve terminal 88 and are controlled by themicrocontroller 42 a in response to signals received from the flowsensors 30 a-30 c. In the event the flow of catalyst as detected by theflow sensor 30 a is below the desired minimum flow and/or flow ofcatalyst occurs through the flow sensor 30 b and 30 c, the valve 84 willopen to supply air to the whistle 80.

The indicators 70 a-70 c and alarm 80 are desirably only activated whena spraying operation is being conducted. As mentioned above, exhaust airof the applicator device is harnessed and routed to the applicator airinput 58 of the array 30 to be used to indicate to the array 30 when aspraying operation is being conducted. This input air is utilized by thearray 30 to connect the indicators 70 a-70 c and the solenoid valve 84to the circuit board 42 to arm them for use. With reference to FIG. 4,this may be accomplished as by routing the air from the air input 58 viatubing 90 to an air pressure sensor 92. The microcontroller 42 a readspressure signals from the sensor 92. When a sufficient pre-selected airpressure corresponding to a spraying operation is sensed, the indicators70 a-70 c and the solenoid valve 84 are activated. A sensitivityadjustment for adjustment of the pre-selected air pressure may beincorporated.

FIG. 10 depicts an example of flow chart of alarm logic implemented bythe microcontroller 42 a in operation of the flow sensor array 30. Forexample, in a first step 100 electrical power is supplied to the circuitboard 42 and in step 102 the air pressure sensor 92 monitors any exhaustair pressure of a spraying operation. When a sufficient pre-selected airpressure corresponding to a spraying operation is detected by the airsensor 92 (step 104) the indicators 70 a-70 c and the solenoid valve 84are activated (step 106). For example, the sensor 92 may sensesufficient air pressure if three consecutive pressure pulses are sensed.

As seen in step 108, catalyst flow is monitored by the flow sensors 30a-30 c. As will be noted, the indication of an active spraying operationrequires a flow of catalyst to the sprayer/applicator. Step 110 relatesto the operation of the flow sensor 30 c. If catalyst flows from theoverpressure outlet 54 c to the flow sensor 30 c this will be detectedand the indicator 70 c illuminated and the solenoid valve 84 activatedto supply air to the whistle 80 (step 112). The whistle 80 and theindicator 70 c should alert the operator to cease the sprayingoperation, which results in a cessation of exhaust air to the applicatorair input 58. In the event cessation of air flow is not detected, theindicator 70 c remains illuminated and air continues to be supplied tothe whistle 80. Once a cessation of air flow has been detected, such asfor three seconds, as seen in step 114, the microcontroller 42 a willactivate the solenoid valve 84 to stop air flow to the whistle 80 (step116). If the issue is corrected, the operator can turn off the indicator70 c (steps 118 and 118 a) and the microcontroller 42 a awaitsre-activation (return to step 102). If the issue is not corrected, thespraying operation is deemed ended (step 120). If spraying resumes, thefail state is reset.

Returning to step 110, if the flow sensor 30 c does not detect anover-pressure condition, the process proceeds to step 122 which relatesto operation of the flow sensor 30 b. If catalyst is flowing from therecirculation outlet 54 b to the flow sensor 30 b this will be detectedand the indicator 70 b illuminated and the solenoid valve 84 activatedto supply air to the whistle 80 (step 124). The whistle 80 and theindicator 70 b should alert the operator to cease the sprayingoperation, which results in a cessation of exhaust air to the applicatorair input 58. Once a cessation of air flow has been detected, such asfor three seconds, as seen in step 126, the microcontroller 42 a willactivate the solenoid valve 84 to stop air flow to the whistle 80(return to step 116). In the event cessation of air flow is notdetected, the indicator 70 b remains illuminated and air continues to besupplied to the whistle 80.

Returning to step 122, if the flow sensor 30 b does not detectrecirculation flow, the process returns to step 128, which relates tooperation of the flow sensor 30 a. If the flow rate of catalyst throughthe sensor 30 a is below the desired minimum flow, this will be detectedand the indicator 70 a illuminated and the solenoid valve 84 activatedto supply air to the whistle 80 (step 130). The whistle 80 and theindicator 70 a should alert the operator to cease the sprayingoperation, which results in a cessation of exhaust air to the applicatorair input 58. Once a cessation of air flow has been detected, such asfor three seconds, as seen in step 132, the microcontroller 42 a willactivate the solenoid valve 84 to stop air flow to the whistle 80(return to step 116). In the event cessation of air flow is notdetected, the indicator 70 a remains illuminated and air continues to besupplied to the whistle 80.

FIG. 11 depicts another example of a flow chart of alarm logicimplemented by the microcontroller 42 a in operation of the flow sensorarray 30. For example, in a first step 200 electrical power is suppliedto the circuit board 42 and in step 202 the air pressure sensor 92monitors any exhaust air pressure of a spraying operation, which exhaustair is delivered in pulses from the spray equipment.

When a first pulse of air pressure is detected by the air sensor 92(step 204), a measurement of the cycle rate of air pressure pulsesdetected by the air sensor 92 begins (step 206). If a second pulse ofair is detected (step 208), a determination of the time betweendetection of the first pulse of air and the second pulse is made andcompared to a predetermined time between pulses, such as 10 seconds(step 210). If the time between pulses exceeds the predetermined time,then a disarm command is sent (step 212) and the process returns to step202. If the time between pulses does not exceed the predetermined time,then a time corresponding to the determined time from step 210 is set instep 214 as the cycle rate of the exhaust air pulses and the indicators70 a-70 c are cleared (step 216) and the indicators 70 a-70 c and thesolenoid valve 84 are activated (step 218).

Once the indicators 70 a-70 c and the solenoid valve 84 are activated,the cycle rate of the exhaust air pulses is monitored (step 220) andcompared (step 222) to the rate set in step 214. If the cycle rate doesnot exceed the rate set in step 214, monitoring continues. If the rateexceeds the rate, the process proceeds to step 212 and a disarm commandis sent. If the spraying operation continues, a new cycle rate of theexhaust air pulses may be periodically set based on the continuingoperation of the spraying equipment (steps 222 a and 222 b)

In addition, the flow sensors 30 a-30 c are monitored in step 224. Thedecision tree first looks to overpressure flow, then recirculation flow,and then feed flow in order to sound the alerts, but undesired flowsensed by any of the flow sensors 30 a-30 c will trigger the alerts. Instep 226, if catalyst flows from the overpressure outlet 54 c to theflow sensor 30 c, this will be detected and the indicator 70 c isilluminated and the solenoid valve 84 is activated to supply air to thewhistle 80 (step 228). As shown in steps 230 and 232, the whistle 80 isactivated for a desired time period, such as 2 seconds, and then turnedoff.

In step 234, if catalyst flows from the recirculation outlet 54 b to theflow sensor 30 b, this will be detected and the indicator 70 c isilluminated and the solenoid valve 84 activated to supply air to thewhistle 80 (step 236). As shown in steps 238 and 240, the whistle 80 isactivated for a desired time period, such as 2 seconds, and then turnedoff.

In step 242, if catalyst flows from the supply outlet 54 a through thesensor 30 a and this flow rate is at or above the desired minimum flow,the process returns to step 224. If the flow rate is below the desiredminimum flow, this condition represents an interrupted flow of thecatalyst. In such case, the degree of interruption is calculated in step244 and compared to a set point, such as between 0 and 400 ms (step246). If the interruption is less than the set point, the processreturns to step 224. If the interruption is greater than the set point,in step 248 the number of interrupts is determined and then compared instep 250 to a predetermined interrupt number, such as 2. If the numberof interrupts is at or less then the predetermined interrupt number, theprocess returns to step 224. If the number of interrupts is greater thanthe predetermined interrupt number, in step 252 a signal is generatedindicating that catalyst flow has been interrupted and in step 254 theindicator 70 a is illuminated and the solenoid valve 84 activated tosupply air to the whistle 80. As shown in steps 256 and 258, the whistle80 is activated for a desired time period, such as 2 seconds, and thenturned off.

As will be appreciated, the present disclosure advantageously providesflow sensors that enable flow detection utilizing magnetic fields todetect the position of a magnet housed in a float that is affected byfluid flow. Such sensors have been observed to be particularly suitablefor use in determining and monitoring the flow of highly reactivecatalysts for which conventional flow sensors are unsuited.

Further, the disclosure incorporates such flow sensors to providesystems configured for use with catalysts to detect when the flow rateof the catalyst is outside of a desired range, and to alert operatorswhen undesirable flow conditions occur.

The systems employ the use a microcontroller to read the position offloats in a flow sensor array then to alert the operator if anyfail-states exists and which one it is. Additionally, the systemadvantageously does not require any operator input or calibration andcan sense when a spraying operation is active and activate the alertsonly during that time.

The foregoing description of preferred embodiments for this inventionhave been presented for purposes of illustration and description. Theyare not intended to be exhaustive or to limit the invention to theprecise form disclosed. Obvious modifications or variations are possiblein light of the above teachings. The embodiments are chosen anddescribed in an effort to provide the best illustrations of theprinciples of the invention and its practical application, and tothereby enable one of ordinary skill in the art to utilize the inventionin various embodiments and with various modifications as are suited tothe particular use contemplated. All such modifications and variationsare within the scope of the invention.

The invention claimed is:
 1. A liquid flow sensor, comprising: anelongate flow tube having an inlet end and an outlet end and a lip,wherein a liquid flows into the flow tube at the inlet end and exitsfrom the outlet end; a float located in the flow tube and configured forthe liquid flowing in the flow tube to flow around the float, the floatincluding a magnet, wherein a bottom of the float may contact the lip ofthe flow tube and the bottom of the float includes a slot configured toenable the liquid to flow from the bottom of the float past the lip toprevent the float from sealing against the lip; an electrical circuitproximate the flow tube, the electrical circuit including a magneticsensor located proximate the float for sensing a position of the magnetin the flow tube, wherein the position of the magnet in the flow tube isrelated to the position of the float in the flow tube, which is relatedto flow characteristics associated with flow of the liquid through theflow tube; and an alarm that is activated by the electrical circuit inresponse to a signal generated by the magnetic sensor based on a flowcharacteristic of the flow of liquid.
 2. The flow sensor of claim 1,wherein the alarm is activated when the flow of the liquid is below apredetermined minimum flow rate.
 3. The flow sensor of claim 1, whereinthe magnetic sensor comprises a giant magnetoresistance sensor.
 4. Amethod of monitoring flow of a liquid, comprising the steps of: flowinga liquid under pressure through an elongate flow tube having an inletend and an outlet end and a lip, wherein the liquid flows into the flowtube at the inlet end and exits at the outlet end; providing a floatincluding a magnet in the flow tube, the float configured so that theliquid flowing in the flow tube flows around the float, wherein a bottomof the float may contact the lip of the flow tube and the bottom of thefloat includes a slot configured to enable the liquid to flow from thebottom of the float past the lip to prevent the float from sealingagainst the lip; directing the flow of liquid through the elongate flowtube to contact and flow around the float such that the position of thefloat in the flow tube is dependent upon the flow of liquid through theflow tube; sensing a position of the magnet in the flow tube, whereinthe position of the magnet in the flow tube is related to the positionof the float in the flow tube, which is related to flow characteristicsassociated with flow of the liquid through the flow tube; and activatingan alarm in response to a sensed position of the magnet.
 5. The methodof claim 4, wherein the step of activating the alarm is performed whenthe sensed position of the magnet corresponds to the flow of liquidbeing below a predetermined minimum flow rate.
 6. The method of claim 5,wherein prior to activation of the alarm, the flow of the liquid mustfirst be at or above the predetermined flow rate.
 7. The method of claim4, wherein the liquid comprises a catalyst liquid.
 8. The method ofclaim 7, wherein the catalyst liquid comprises methyl ethyl ketoneperoxide.
 9. The method of claim 4, wherein the sensing of the positionof the magnet is performed by a giant magnetoresistance sensor.
 10. Themethod of claim 4, further comprising a visual alert that is activatedif flow of the liquid is detected to be below a predetermined minimumflow rate.
 11. A flow monitoring system, comprising: a source ofpressurized liquid capable of providing a feed flow of the liquid, or arecirculating flow of a liquid, or an overpressure flow of the liquid,or combinations thereof; a first flow sensor for receiving the feed flowof the liquid, a second flow sensor for receiving the recirculating flowof the liquid, and a third flow sensor for receiving the overpressureflow of the liquid, each of the first, second and third flow sensorscomprising a flow tube having a float located in the flow tube andconfigured for liquid flowing in the flow tube to flow around the float,each float including a magnet; an electronic circuit including: (i) afirst magnetic sensor located proximate the first flow sensor forsensing a position of the magnet in the float of the first flow sensor,wherein the position of the magnet in the flow tube of the first flowsensor is related to flow characteristics associated with the feed flowof the liquid through the first flow sensor, (ii) a second magneticsensor located proximate the second flow sensor for sensing a positionof the magnet in the float of the second flow sensor, wherein theposition of the magnet in the flow tube of the second flow sensor isrelated to flow characteristics associated with the recirculating flowof the liquid through the second flow sensor, and (iii) a third flowsensor for sensing a position of the magnet in the float of the thirdflow sensor, wherein the position of the magnet in the flow tube of thethird flow sensor is related to flow characteristics associated with theoverpressure flow of the liquid through the third flow sensor; and afirst alarm that is activated if the first flow sensor detects flow ofthe feed flow below a predetermined minimum flow rate, a second alarmthat is activated if the second flow sensor detects flow of therecirculating flow, and a third alarm that is activated if the thirdflow sensor detects flow of the overpressure flow.
 12. The system ofclaim 11, wherein the liquid comprises a catalyst liquid.
 13. The systemof claim 12, wherein the catalyst liquid comprises methyl ethyl ketoneperoxide.
 14. The system of claim 11, wherein the first, second, andthird magnetic sensors each comprise a giant magnetoresistance sensor.